This invention relates to a belt assembly which, in operation, can be tensioned along a path, comprising a belt having a toothed surface and an oppositely located back surface, and one unit or a plurality of units fastened to the belt on the side of the back surface.
Such a belt assembly is utilized in practice, for instance in apparatuses for preparing items to be mailed, for the purpose of conveying postal items located on a transport surface. The unit fastened to the belt is often a carrier. The carriers extend through the slots provided in the transport surface and move forward the postal items to be conveyed as required, for instance stepwise.
The advantages of a belt assembly over the conveyor chains utilized heretofore, such as link chains of the bicycle-chain type, are important.
Firstly, belts make less noise and are lighter than chains. Owing to the smaller mass of the belts, the acceleration and retardation forces are smaller, so that the drives and slip-action clutches can be of lighter construction.
Secondly, unlike chains, belts need not be lubricated. Lubricated chains entail the risk of the postal items becoming dirty.
However, the belts used heretofore in apparatuses for preparing items to be mailed also have a number of disadvantages which are not inherent to conveyor chains and form an obstacle to the progressive introduction of the belt.
The most important disadvantage is the fact that the belts must be manufactured as endless belts with the carriers provided at predetermined positions. The carriers are connected to the back surface of the belt, for instance by means of glue or by ultrasonic welding, and the end parts of the belt are similarly connected to each other. This means that both the length of the endless belt and the position of the carriers are fixed and that for each type of apparatus for preparing items to be mailed, specific belts must be manufactured and kept in stock for service.